Direct-positive images by the silver salt diffusion process



United States Patent 6 Claims. 61. 9629) I This invention relates to a process for the production of direct-positive images as well as to a photographic material for accomplishing this process.

It is known that in the silver salt diffusion process, the unexposed portions of the silver halide are dissolved after or during the development and the dissolving silver salts are introduced into a second layer containing nuclei on which the dissolved silver saltsare reduced by the processing liquid to silver. There is thus obtained a positive image of the copied original in the nuclei-containing layer.

Itis also known so to arrange the two layers that the nuclei-containing layer is cast onto the light-sensitive silver halide layer and it is later transferred to another support, e.g., ordinary writing paper.

According to US. Patent 2,725,298, the layer combination is first of all processed and only after the positive has been formed in the nuclei-containing layer is this layer then transferred in a separate working step from the negative layer to another support. It has already been pointed out in German Patent 974,191 that the two working steps can be combined. This can be achieved, for example, by using an apparatus such as that employed for the production of images by the silver salt diffusion process. The support carrying the negative layer and the nuclei-containing layer is introduced into one entrance slot of such apparatus, and the new support for the nuclei-containing layer into another entrance slot. After both sheets have travelled through the processing liquid, they are pressed together by a pair of rollers. They are then separated and the layer containing the nuclei then adheres to the new support.

If it is desired to use ordinary writing paper as a final support for the positive or nuclei-containing layer, difficulties are met since such papers are not sutficiently resistant to water and do not have suflicient wet strength, become creased and show very strong yellowing. These difliculties can be avoided if only the negative material containing the nuclei layer is moistened. This can be achieved with a suitable developing apparatus having, for example, 2 guiding tracks, whereby the track for the lightsensitive negative material leads the said material through a developing bath, while the other guiding track leads the transfer material below or above the developing bath whereby the transfer material is retained dry until it is contacted with the moistened negative material at a pair of pressure rollers arranged behind the developing bath. Thus, the transfer material which is the final paper support is moistened only on one side. Suitable devices of this type are described, for example, in British Patent Specification 699,085; Belgian Patent Specification 622,297 and 622,298 and the German application G 23,061 (published as Auslegeschrifts No. 1,093,671 and No. 1,086,125). The nuclei-containing layers referred to in the aforementioned two patents are, however, not suitable for this process, since they require too much moisture and too Patented Nov. 12, 1968 We now have found that excellent direct-positive transfer images can be obtained by the use of a multilayer material consisting of a supported light-sensitive layer and an uppermost transfer layer coated on the said light-sensitive layer.

The light-sensitive layer consists of a hardened silver halide gelatine emulsion layer, containing as silver halides, silver chloride or silver bromide or mixtures thereof. The emulsion layer may also contain a small amount up to 5 %of silver iodide. Preferred are emulsions in which the halide substantially consists of silver chloride, The term hardened gelatine layer refers to a gelatine layer treated with the usual hardening agent such as formaldehyde, mucochloric acid, glyoxal or the like and having a softening point of not below C. The light-sensitive layer should contain approximately 0.5-1.5 g. silver/m The transfer layer contains as binding agent salts of alginic acid with alkali metals, the so-called alginates, preferably sodium alginate or combination of the said alginates with other hydrophilic binders such as polyvinylalcohol, gelatine, carboxymethyl cellulose or esters of alginic acid. The binding agent of the transfer layer should contain 100-25 of alginates. The dried transfer layer is very thin and contains approximately 0.3-5 g. alginate per square meter.

Even very low concentrations of alginates produce very viscous solutions so that the silver halide layer can be provided with an alginate layer which is very thin when dry.

Alginate layers swell very quickly in the alkaline processing liquid and since they are very thin, they only slightly impede the penetration of the processing liquid into the silver halide layer.

Although any sheet-like material can be used as support for the said layers, we prefer a usual paper support.

The layers of alginates are, however, also characterised by the fact that they adhere badly to hardened gelatine layers, and this property appears independent of the moisture content of the layers. On the other hand, alginate layers adhere very satisfactorily to paper. The adhesion of the alginate layer to the paper is always better than to the gelatine layer, even when the layers have become dry before separation.

The developing nuclei, for instance colloidal distributed noble metals such as silver, gold and the like or sulphides, for example, of silver, zinc or sodium, which are necessary for the instant process can be present either in the said transfer layer of alignates or in the final paper support onto which the alginate layer is to be transferred. If the developing nuclei are added to the alginate layer, the silver salts diffusing out of the unexposed areas of the silver halide layer are precipitated as silver.

If the previously described alginate layers or binder combinations with alginates do not contain any nuclei, and provided they are sufliciently thin, they allow rapid diffusion of the dissolved silver salts originating from the silver halide layer. For example, these silver salts can also be caused to deposit silver on the surface of the final paper support if nuclei have been added to the paper composition or to the sizing of the paper. In this case, the alginate layer serves to provide a close contact between silver halide layer and the paper. Silver halide gelatine layers without an alginate layer have such a poor contact to common papers that the diffusion of the silver salts is only possible in spot-s. The alignate layer can be transferred on to any common writing or typewriting paper.

The layers of the present invention are processed in an alkali developer which contains a silver salt solvent, e.g., thiosulphates of alkali metals or of ammonium ions; preferred is sodium thiosulphate. If required, such a silver salt solvent can also be added to the writing paper (to which the transfer is to be made) at the time of manufacture; the addition to the developer is then superfluous.

In order to improve the color of the resulting positive image, it is also possible to add socalled blue toners to the alginate layers, which toners so influence the deposition of the silver that the color of the silver image is changed from brown to'bluish-black.

The process according to the invention is more fully explained in the following examples:

EXAMPLE 1 A silver chloride emulsion layer, such as used for the Copyrapid process, has cast thereon a solution of the fol lowing composition:

Water l 1 Sodium alginate, e.g., Algipon 778 of Messrs.

Henkel g Ag- S, suspended in 4 g. of gelatine gm 50 Wetting and brightening agents can also be added to the solution.

The negative paper produced in this way is developed after exposure in a developing apparatus with a dry slot as already described above. The developer used has approximately the following composition:

Water ml 70 Sodium sulphite g 80 Hydroquinone g Phenidone g 1 KBr g 2 NaOH g 10 Nagszog g 8 made up to 1 litre.

Writing paper is guided through the dry slot and pressed against the developed negative at the squeezing rollers. After separation, the alignate layers has transferred to the writing paper and forms a positive image thereon.

EXAMPLE 2 A silver chloride emulsion layer, such as used as negative material for the Copyrapid process, is coated with the following solution:

Water l 1 Sodium alginate, e.g., Manucol SS/LF 0f A.I.L. g 15 Polyvinyl alcohol, e.g., Moviol Far-bwerke Hoechst A.G. g 10 Ag S, suspended in 4 g. of gelatine mg 50 A 1% solution of phenyl mercaptotetrazole as blue toner ml 3 Wetting and brightening agents can also be added.

The negative is processed in the manner described in Example 1.

Similar results are obtained if the following combinations of alginates with other binding agents are used:

Sodium alginate in g.: Other compounds A commercial Copyrapid negative material is provided with a thin alginate layer which swells strongly in the developers previously described. In addition, a writing paper is impregnated with a colloidal Ag S solution, which is obtained by adding 3 ml. of 0.1 NAgNO and 3 ml.

of 0.1 NNa S, to 100 ml. of 0.5% gelatine. After being dried, the writing paper is processed with the negative in the manner already described in Example 1. There is thereby formed a dark grey positive image on the writing paper.

EXAMPLE 4 A. normal Copyrapid negative is. provided with a strongly swelling thin layer of sodium alginate containing 1% of an alginic acid este r, for example, Algitex, an alginic, acid, propylenglycolester of the firm Henkel .Cie. The negative is processed in the manner indicated vin Example l with a sized paper, the sizing composition having been provided during manufacture with colloidal Ag S. Such a quantity is added that, after manufacture, about 0.02 to 0.05 g. of Ag S are provided per square metre.

A positive image is formed on the writing paper.

I EXAMPLE 5 i A normal Copyrapid negative is provided with a thin, strongly swelling alginate layer. In addition, the sizing composition of an art printing paper has colloidal Ag S and some Na S O -5H O added thereto.

The quantities of the additives are so chosen that, after production, about 0.020.05 g. of Ag S and 1-2 g. of Na S O -5H O are provided per square metre of the prepared paper layer. The two papers are processed with a normal Copyrapid developer in a developing apparatus with a dry slot as in Example 1. A positive image of excellent quality is obtained on the final support.

We claim:

1. In the process of preparing a photocopy by the silver salt diffusion process using a supported light-sensitive silver halide emulsion which in turn supports a transfer layer that is originally held only on the emulsion but as part of the processing is transferred to a separate support on which the desired positive image is finally carried, the improvement according to which the transfer layer is essentially an alkali metal alginate transfer layer, and the emulsion is in hardened gelatin that has a softening point at least as high as 100 C. I

2. The combination of claim '1 in which the transfer layer also contains development nuclei for the silver halide.

3. The combination of claim 1 in which the separate support is a paper sheet the surface of which contains development nuclei for the silver halide. I

4. A silver salt diffusion material in the form of a support carrying a light-sensitive hardened silver halide emulsion in gelatin having a softening point atleast as high as 100 C., the emulsion in turn supporting a transfer layer that is essentially an alkali metal alginate transfer layer.

5. The combination of claim 4 in which the transfer layer also contains development nuclei for the silver halide. I t i 6. The combination of claim 4 in which the transfer layer is essentially free of development nuclei.

References Cited UNITED STATES PATENTS 7/1951 Land Q 96-29 7/1953 Land 9629 12/1954 Land 9629 FOREIGN PATENTS 11/1960 Germany.

OTHER REFERENCES NORMAN G. TORCHIN, Primary Examiner.

G. COHN, Assistant Examiner. 

1. IN THE PROCESS OF PREPARING A PHOTOCOPY BY THE SILVER SALT DIFFUSION PROCESS USING A SUPPORTED LIGHT-SENSITIVE SILVER HALIDE EMULSION WHICH IN TURN SUPPORTS A TRANSFER LAYER THAT IS ORIGINALLY HELD ONLY ON THE EMULSION BUT AS PART OF THE PROCESSING IS TRANSFERRED TO A SEPARATE SUPPORT ON WHICH THE DESIRED POSITIVE IMAGE IS FINALLY CARRIED, THE IMPROVEMENT ACCORDING TO WHICH THE TRANSFER LAYER IS ESSENTIALLY AN ALKALI METAL ALGINATE TRANSFER LAYER, AND THE EMULSION IS IN HARDENED GELATIN THAT HAS A SOFTENING POINT AT LEAST AS HIGH AS 100%*C. 